The present invention relates to a method for smelting copper sulfide bearing sulfide concentrates, in which method the slag obtained from the smelting process is treated in at least one hydrometallurgic step.
For treating primary copper raw materials, there are mainly two principal lines. One is the concentration-smelting-electrolytic refining line, and the other is leaching, such as the heap leaching-liquid-liquid extraction and electrolytic recovery line. With respect to reasons connected to raw material quality, environmental protection, geography and economy, both processing lines are meeting growing difficulties.
When starting to concentrate copper-based raw materials, we often face a situation where the majority of the mineralization is oxidized and possibly difficult to flotate. Among these are particularly copper ore deposits containing copper silicates and iron oxides. Also mixed structures with copper sulfide and pyrite may be nearly impossible with respect to flotation. A specific group of problems is represented by finely divided, often pyritic copper-zinc-lead ore deposits. The treatment of said ore deposits by traditional methods usually renders a fairly weak result as regards recoveries and concentrate contents. When the transport expenses to the refinery often are too high even with a high-quality concentrate, they are even more so with a low-quality concentrate. What is more, in that case environmental hazards are increased at two separate locations, for instance because of arsenic. The smelting process itself typically includes many steps, among them smelting for example in a flash smelting furnace, converting, anode furnace treatment; sulfuric acid production for gases, and electric furnace or concentration process for slag. The copper raw material may also be so rich or so poor in iron, that it is turned directly into raw copper, i.e. blister copper, in one smelting step. In that case the obtained slag is conducted to an electric furnace for reduction. From the reduction process, there is obtained a molten copper-iron mixture that is conducted into converting, and slag containing over 0.5% copper. As an alternative, the electric furnace slag is conducted into a concentrator in order to recover the rest of the copper, in which case in the electric furnace, there is produced blister copper that is suited in an anode furnace. Owing to the high copper content of the slag from direct blister copper smelting, being generally 12% by weight or more, and owing to the often high impurity contents, the investments required for this kind of processes are high, and so are the operating costs, for example owing to the price of electricity.
As regards the second prevailing method—processing based on heap leaching—it is likewise facing harder times. As long as the ore neither contains remarkable amounts of precious metals nor remarkable amounts of copper as chalcopyrite, CuFeS2, or as some other component that is hard to dissolve, the situation is fairly good. However, as a rule, a growing share of raw materials even in already functioning mines is particularly formed of slow-dissolving copper minerals. This means increasing costs. Said other method also has another drawback, one to which already built plants gradually have to adjust—i.e. the restricted lifetime of nearly all mines. If the whole process chain from the mine to cathode copper is based on one deposit only, the plant generally faces an unsound situation, as the volume of the ore deposit is gradually used up. As a result, the return of the invested capital is not optimal.